Page 37 - The Handbook of Persuasion and Social Marketing

30 The Handbook of Persuasion and Social Marketing

(Kelman & Hovland, 1953; see Petty & Wegener, 1998a, for a review).
Source credibility is used to refer to two aspects of the source: the expertise
of the source (i.e., the amount of knowledge the source possesses on the
message topic) and the source’s trustworthiness (i.e., the motivation of the
source to be honest about the information delivered). Expertise increases
the credibility of a source because it enhances a source’s ability to convey
information that is accurate; trustworthiness increases the credibility of a
source because it suggests that the source is motivated to share truthful
information. Early research found that audiences were more persuaded
when the source of a message was an expert (Rhine & Severance, 1970) or
viewed as trustworthy (Mills & Jellison, 1967).
Researchers have catalogued a number of other aspects of the source
that affect persuasion, independent of source credibility. For example, past
research has found that people’s attitudes are influenced by the physical
attractiveness of a source. Attractive sources have been shown to enhance
persuasion compared to unattractive sources (Snyder & Rothbart, 1971).
In addition, a source’s power—his or her control over resources—can af-
fect persuasion. Powerful sources have been shown to produce more atti-
tude change than powerless sources (e.g., Festinger & Thibaut, 1951;
French & Raven, 1959; see Briñol & Petty, 2009a, for a review). Similarly,
sources might vary on how warm or competent they are perceived to be
(Aaker, Vohs & Mogilner, 2010) or how liked they are (Petty, Cacioppo &
Schumann, 1983). In each of these cases, a property of the source influ-
ences the extent of attitude change, and it may or may not matter what the
source says. Although initial research on source factors focused on effects
of sources that were consistent with their valence (i.e., credible, attractive,
and powerful sources increased persuasion), in the following sections, we
review research showing that source factors can produce various effects
depending on the circumstances. This means that positively valenced
source factors can sometimes be associated with increased persuasive im-
pact, but at other times these very same aspects of the source can be as-
sociated with decreased persuasion.

Message Factors in Persuasion

Messages factors constitute what is literally said or spoken in the message
or how the message is structured or organized. One important aspect of
the information contained in the message itself is how compelling the ar-
guments provided are. Strong arguments tend to present consequences
that are highly desirable, likely to occur, and important (Petty & Wegener,
1998a). If people are carefully thinking about a message, the quality of the